1. Field of the Invention
The present invention relates to a slider device and a measuring instrument.
2. Description of Related Art
There has been known a rack and pinion mechanism in the prior art, and also there has been known a slider device driven by this rack and pinion mechanism (refer to, for instance, Patent document 1: Japanese Patent Publication No. 3133005, and Patent document 2: Japanese Patent Laid-Open Publication No. 2001-151465).
A slider device based on the conventional technology is shown in FIG. 7.
A slider device 900 includes a longitudinally extended base 910 having a flat upper surface, a running head 920 running back and forth along a longitudinal direction of the base 910, a guide mechanism 930 for guiding a running direction of the running head 920, and a driving unit 940 for driving the running head 920.
The guide mechanism 930 includes two rails 931, 932 laid in parallel to each other on the upper surface of the base 910 and sliders 933, 934 provided over and sliding on the rails 931, 932. The sliders 933, 934 are attached to a bottom surface of the running head 920, and the running direction is guided by sliding those sliders 933, 934 along the rails 931, 932.
The driving unit 940 is provided between the two rails 931, 932 and includes a rack 941 provided in parallel to the rails 931, 932, a pinion 942 engaging with the rack 942, a motor 943 for rotatingly driving the pinion 942
The motor 943 is fixed on the running head 920, and a rotor of the motor 943 is connected to the pinion 942.
A tooth surface of the rack 941 is provided on one side surface of the rack 942 (a surface facing either one of the rails), and a direction of rotation axis of the pinion 942 is perpendicular to an upper surface of the base 910.
In such a configuration, when the motor 943 rotates for driving, the pinion 942 is rotated. Then, the pinion 942 moves along the rack 942 because of engagement with the rack 941. The running head 920 runs with the motor 943 as the pinion moves. A direction of the running head 920 is guided along the direction of the rails 931, 932 as the running head 920 runs along the rails 931, 932.
However, since an orbit of the pinion 942 follows the tooth surface of the rack 941, if there is an error in accuracy such as irregularities of the rack's tooth surface, the pinion 942 is swung in a direction orthogonal to the rack 941, and the orbit of the pinion 942 starts vibrating. When the pinion 942 is swung in the direction orthogonal to the rack 941, the running head 920 is also swung in the same direction, so that the running accuracy of the running hear 920 is disadvantageously degraded.
It is principally possible to (forcibly) restrict the running direction of the running head 920 in a direction along the rails 931, 932 simply by improving the engagement accuracy between the rails 931, 932 and the sliders 933, 934 in the guide mechanism 930. However, driving units (such as a rack, a pinion, and a motor) are broken, and there occurs the problem that loose engagement is generated. On the contrary, when the pinion 942 is swung in the direction orthogonal to the rack 941 and a stress in the direction orthogonal to the rack 941 is generated, as the direction is orthogonal to the direction of guidance by the guide mechanism 930 (rails and sliders), a large stress is loaded to the guide mechanism 930 (rails and sliders). When a stress is loaded to the guide mechanism 930, durability and accuracy of the guide mechanism 930 (rails and sliders) are disadvantageously spoiled.